HDAC9 and acute myeloid leukemia: Sapacitabine has demonstrated clinical activity in a phase I study involving leukaemia patients (Kantarjian et al, 2010), whereas the HDAC inhibitors vorinostat and valproate have also elicited clinical responses in AML patients in phase I studies (Bug et al, 2005; Garcia-Manero et al, 2008).